1. Field of the Invention
The present invention generally relates to light emitting diode (LED) packaging, and more particularly to light emitting diode (LED) wafer-level chip scale packaging (WL-CSP) for enhancing heat conduction.
2. Description of the Prior Art
Light emitting diode (LED) is a device that transforms electric power into light source. Compared with conventional light sources, the LED has advantages of low input voltage, low power consumption, and quick response time. Furthermore, the LED has other beneficial characteristics, such as light weight, low cost to manufacture, and capability of mass production. Accordingly, the LED has become an indispensable element in the modern life, especially in the electronic, communication, and consumer products fields.
One of the main purposes of semiconductor packaging is to protect the circuit chip from being damaged physically or chemically, ensuring the proper functionality of the integrated circuit. The selection of the packaging material is very important not only to meet the protection requirement, but also to enhance the reliability and functionality of the integrated circuit.
As the LED becomes more high-power, more heat is therefore generated, which disadvantageously leads to worsened characteristics, declined intensity, and even burnt-out device. Conventionally, the LED packaging seldom concerns the heat dissipation, which is at most treated in printed circuit board (PCB) level or in system level, albeit still not effectively solves the heat dissipation problem. Some exemplary heat-dissipating packaging designs and corresponding circuits are disclosed in U.S. Pat. No. 6,498,355 entitled ‘High Flux LED Array’ and are reproduced in FIG. 1A to FIG. 1C.
As shown in FIG. 1A, an LED 4 is flipped on a printed circuit board, which consists of a dielectric layer 10 and conductive trace 8. The printed circuit board (8, 10) further overlies a metal substrate 6. The heat generated by the LED 4 is conducted through a thermal contact 20 and thermally conductive material 24, and finally to the metal substrate 6. The heat is further conducted through the via 12 in the printed circuit board (8, 10), which is filled with thermally conductive material.
FIG. 1B shows another arrangement for dissipating the generated heat. Compared with that in FIG. 1A, a submount 30 is inserted between the LED 28 and the PCB (8, 10), and power channels 40 are devised within the submount 30 to facilitate the electrical power connection between the LED 28 and the conductive trace 8. Similar to FIG. 1A, the heat generated by the LED 28 is conducted through a thermal contact 46 and thermally conductive material 24, and finally to the metal substrate 6. The heat is further conducted through the via 12 in the printed circuit board (8, 10).
FIG. 1C shows a further arrangement for dissipating the generated heat. Compared with that in FIG. 1B, the electrical power connection is accomplished by way of bonded wires 5, instead of power channels. Similar to FIG. 1A or FIG. 1B, the heat generated by the LED 28 is conducted through a thermal contact 46 and thermally conductive material 24, and finally to the metal substrate 6. The heat is further conducted through the via 12 in the printed circuit board (8, 10).
The packaging designs mentioned above suffer the disadvantage of having a packaging area far greater than the LED area. The number of the LEDs that the submount 30 can hold is therefore greatly restricted, even those packaging designs somewhat improve the heat dissipation.
For the reason that conventional LED packaging could not effectively solve the heat dissipation problem, a need has arisen to propose a novel LED packaging to effectively conduct the heat generated from the LED and increase the number of LEDs per packaging area, thereby improving the efficiency of the LED.